1. Field of the Invention
The present invention relates to a gas flow simulation method. More particularly, the present invention relates to a gas flow simulation method for simulating the behavior of a gas flow flowing along the surface of the spherical model when the imaginary object model such as spherical model flies in rotation in a gas. To this end, imaginary object model such as a spherical model having concavities or grooves formed on the surface thereof is set by means of a computer.
2. Description of the Related Art
It is known that turbulence of a gas flow such as separation of a gas occurs on the periphery of an object such as a sphere that is used in a ball game, while the sphere is flying in the gas. In the case where there is a change in the configuration of the surface of the sphere or in the case where the sphere is flying in rotation, the turbulence of the gas flow becomes more complicated. The turbulence of the gas flow affects the flight performance of the object and in particular, the flight distance of the sphere such as a ball which is used in ball games.
For example, in the case of the golf ball, a large number of dimples (concavities) formed on the surface thereof affect its aerodynamic characteristic greatly. Thus it is important to recognize the casual relation between the aerodynamic characteristic of the golf ball and the size of the dimples, the arrangement thereof as well as combinations of the dimples having various sizes and configurations. It is frequent that a high-class player applies a backspin to the golf ball intentionally. Thus it is particularly important to recognize the aerodynamic characteristic of the golf ball during its rotation.
To evaluate how the flight characteristic of the golf ball changes according to the difference in the size of the dimples formed on the surface of the golf ball, the arrangement thereof as well as combinations of the dimples having various sizes and configurations, many golf balls having different dimple specifications are made on an experimental basis, and experiments of hitting the golf balls thus made are conducted to measure flight distances thereof and the like. In this manner, the aerodynamic characteristic of the golf ball is determined. In recent years, there are proposed methods and apparatuses of measuring the lift and drag coefficients of the golf ball and spheres to analyze the aerodynamic characteristic thereof by placing them in a wind tunnel instead of conducting ball-hitting experiments.
Disclosed in Japanese Patent Application Laid-Open No. 6-194242 is the method and apparatus for measuring the drag and lift thereof by utilizing a wind tunnel to analyze the aerodynamic characteristic of the golf ball. As shown in FIG. 30, in the measuring apparatus 1 placed in the wind tunnel together with the golf ball, the motor 3 rotates the aluminum shaft 2 having the object T such as the golf ball installed on its upper end to measure its flight characteristic, and the strain of the aluminum shaft 2 is detected by the strain-type detector 4, for detecting the axial three components of a force, disposed on the periphery of the aluminum shaft 2. When the object T is rotated in an gas flow generated in the wind tunnel, the object T in the wind tunnel has a state pseudo to an actual flight state. The lift coefficient of the object T and its drag coefficient are derived from a measured strain amount of the aluminum shaft 2 to analyze the flight characteristic of the object T. In the measurement which is performed by the measuring apparatus 1, gas flows are generated in various conditions in the wind tunnel and the aerodynamic characteristic can be measured in various conditions.
To select the configuration and the like of the dimple simply and effectively, the experimental method of forming concavities and convexities on the rotating sphere is proposed in Japanese Patent Application Laid-Open No. 6-194242. The method necessitates preparation of models on an experimental basis, thus leading to a high cost and much time.
In the measurement of the aerodynamic characteristic of the golf ball by conducting experiments of hitting the golf ball made on an experimental basis and of placing the golf ball in the wind tunnel, it is difficult to make the golf ball on an experimental basis in the case where concavities or grooves are formed on the surface of an object to be measured in its flight performance and also difficult to prepare a large number of objects having different patterns in the disposition and size of the concavities or grooves and accumulate data obtained from the measurement. Thus the proposed measuring method and apparatus has a problem that it is impossible to make a detailed analysis as to how the gas flow is affected by the configuration and size of individual dimples formed on the surface of the golf ball and the arrangement of the dimples.
The conventional method of evaluating the aerodynamic characteristic of the golf ball is capable of evaluating characteristics of the gas flow after it changes but is incapable of clarifying the casual relation between the configuration of a newly designed dimple and the aerodynamic characteristic. Therefore frequently, the newly designed golf ball has performance different from the desired performance. In this case, a re-designed golf ball is made on an experimental basis to check the aerodynamic characteristic thereof. As such, the conventional measuring method and apparatus has a problem that it takes much time and money to develop a golf ball having a new specification of dimples.
The aerodynamic characteristic of an object is evaluated not by making it on an experimental basis but by a simulation using a computer. But the conventional simulation method is incapable of accurately expressing the motion of the object flying in rotation in a gas by simulation and apprehending the aerodynamic characteristic thereof. It is very difficult to express the motion of the sphere such as the golf ball having concavities or convexities formed thereon, when it flies in rotation in the gas.